Optical lens and similar device



SR 012 09 zaw wf A. W. KINGSTON OPTICAL LENS AND SIMILAR DEVICE March23, 1943.

T/azg Filed June 8, 1936 -INVENTOR Patented Mar. 23, 1943 UNITED STATESSearch Room OPTICAL LENS AND SDVHLAR DEVICE Arthur William Kingston,London, England, as-

signor, by direct and mesne assignments, to Combined Optical IndustriesLimited, London,

England Application June 8, 1936, Serial No. 84,170 In Great BritainFebruary 23, 1934 8 Claims.

This invention relates to a method of manufacturing optical devices foruse in instruments of precision and to the devices manufactured inaccordance therewith. This is a continuation in part of my application,Serial No. 735,592, filed July 17, 1934.

According to thrspresent invention a method of manufacturing opticaldevices is characterised in that a transparent the noplastwmatgrialisgiven by a single mouldii g operation the shape and highlypolishedsurface necessarymsuch use by being pressed between dies ofknown type but having surfaces polished to a degree not hereto foredisclosed or practised, such pressing being done at a temperaturesufficiently low not to injure such highly polished surfaces of thedies.

According to another feature of the invention there is provided anoptical device for use in instruments of precision comprising a mouldedstructure composed of an organic, plastic, transparent materialcharacterised in that it sets and conforms accurately to the opticallypolished surfaces of a die.

By optical devices Lm ean lenseiprism s, mir- WWto refract or 'fe'fiectgh w sui a e for use in instruments of precision such as cameras, fieldand opera glasses, telescopes, microscopes, projectors and the like, butI do not include lamp glasses, rough lenses or reflectors such as arecommonly used in electric torches or other hand lamps where the opticalperfection is of small importance and which are therefore not providedwith optically polished surfaces.

By optically polished I mean having such a degree of polish as is notless than that found upon the surface of glass lenses used ininstruments of precision today. The higher the polish the better will bethe resulting lens.

By moulding I mean any process whereby the required shape in threedimensions is imparted to the raw material by dies exerting a pressure.

By transparent material" I mean one through which light will pass to adegree comparable with that of ordinary glass.

Transparent materials which are sufficiently plastic to be moulded at atemperature between 100 C. to 150 C. which temperature is sufficientlylow as not to injure the optical polish on a diesurface are commerciallyavailable today. Such material may be a cellulose derivative or asynthetic resin, and these materials can readily be moulded at therequired temperature and there is no distortion in the structure as thematerial cools. Examples of these materials are a polymerise .an acrylicacid resin which are sold respectively under the names of "Trolitul andPerspex. Optical devices made of these materials are superior to thosemade of glass because their transmission of the violet end of thespectrum is high. For example, whereas ordinary crown glass passes only20% of ultra violet light Perspex passes 70%.

Specific embodiments of the present invention will now be described withreference to the ac companying drawing of which Figure 1 shows acombined lens and mount;

Figure 2 shows a modified form of combined lens and mount;

Figure 3 is a diagrammatic view of a press for moulding the lenses;

Figures 4-7 are side elevations in section of various forms of lenses;

Figure 8 is a side elevation of yet a further modification partly insection taken along the line 8-8 of Figure 9.

Figure 9 is a front elevation of the modification shown in Figure 8.

Figures 10 and 11 are respectively a front and side elevation of yet afurther modification.

Figure 12 is a front elevation of a further modification.

Figures 13 and 14 are respectively a side elevation in section and aperspective view of a moulded prism.

Figure 15 is a side elevation in section of a mirror, and

Figure 16 is a sectional elevation of a combined eye-piece and lens.

As shown in Figure l, a moulded structure of transparent organicmaterial comprises a lens 20 and a cylindrical mount 2| surrounding thelens 20 and formed integrally therewith. The portions of the surfaces ofthe dies that form the lens are provided with an optical polish but theportion that forms the mount is not polished and may be provided with amilled or other roughened surface so as to facilitate subsequentstaining of the same to produce opacity. The combined lens and mount mayreadily be introduced into a holder 22 and moved backwards and forwardsrelatively to the holder for the purpose of focussing. It will be seenthat the mount, in addition, constitutes a protecting rim for the lens.

In order to facilitate the movement of the combined lens and mount forthe purpose of focussing. the mount may have a screw-thread 23 mouldedintegrally therewith as shown in Figure 2. The screw-thread 23 isadapted to coact with a groove in the holder, and a collar 24 isprovided to facilitate rotation of the mount and to act as a stop.

A press for moulding the lenses is shown in Figure 3. The press which issecured to a support 25 comprises dies 26 and 21 which are respectivelysecured to rods 28 and 29. The rod 28 is held in a chuck 30 which ismounted on the lower end of a rod 3|, and the rod 3| is adapted to slideup and down in a sleeve 32 which is secured to the support 25. A lever33 which is pivotally secured to a bracket 34 engages a pin 35 securedto the upper end of the rod 3|.

The lower end of the rod 29 is engaged by a lever 36 which is mounted ina similar manner to the lever 33 so that the rod 29 together with thedie 21 can be raised when desired. A collar 31 is provided on the rod 29which engages a plate 38 and acts as a stop to prevent the die 21 frombeing lowered beyond a predetermined point.

A mould casing 39 which co-operates with the dies is secured to thesupport 25, and comprises a sleeve 40 which is in register with the diesand which is surrounded by a jacket 4| for steam or cooling water. Inletpipes 42 and 43 for steam and cooling water respectively are connectedto the casing and are each provided with a valve 44 and 45 forcontrolling the flow of fluid into the jacket. An exhaust pipe 46 forsteam and water is provided on the side of the jacket remote from theinlet pipes.

A jacket 60, similar to the jacket 4| surrounding the die 21, surroundsthe die 26 and comprises inlet pipes 6| and 62 for steam and coolingwater respectively, and an exhaust pipe 63. The inlet pipes are providedwith valves 64 and 65 for controlling the fiow of fluid in the jacket.

The press is operated as follows: The resin or like material of whichthe lens is to be moulded is cut into a number of pellets which will fitinside the sleeve 40. The size of each pellet is accurately calculatedso that it contains sufficient material for the particular lens which isto be made. without having undue waste material. The steam-valves 44 and64 are opened so that steam flows through the jackets 4| and 60 and thedies 26 and 21 are heated. A pellet 41 is next placed in the sleeve 40so that it rests on top of the die 21 which is held by means of thecollar 31 about half way up the sleeve 40. The die 26 is then pressedinto engagement with the pellet by lowering the lever 33 by hand or withthe aid of hydraulic or mechanical means. The die 26 is arranged toengage the pellet with only a light pressure so that the pellet isfurther heated by the hot die 26 before the full pressure is applied. Inaddition to ensuring that the pellet has reached the correct temperaturefor moulding. this method of employing only a light initial pressureobviates the formation of cracks and faults which occur if the fullpressure only is applied.

After the light pressure has been applied for a few seconds the fullpressure is applied and maintained after the pellet has been mouldeduntil it has been cooled by circulating cooling water through the jacket4| in place of steam. This follow-up pressure ensures that the mouldedpellet is always in contact with the dies until it is cool wherebywarping clue to the shrinkage caused by the drop in temperature isprevented and the surfaces of the moulded pellet conform accurately tothe surfaces of the dies. The initial pressure is preferably of theorder of 10% to 20% of the final pressure, for example, a lens of 2square inches area is moulded with an initial total pressure of 1 tonand a final total pressure of tons.

In order to reduce the displacement of the material, caused by the dies,to a minimum, and thereby to obviate the risk of distortion caused bydisplacement, the pellets 41 are preferably preformed so as to conformapproximately, say within a few thousandths of an inch, to the shape ofthe article which is to be moulded.

The preformed pellet is provided with a surface which will engage thedie near the middle thereof so that the displacement of the materialtakes place from the middle towards the edges. For example, with a diehaving a concave spherical surface the pellet is given a convexspherical surface of slightly less radius of curvature. It will be seenthat if the pellet had a flat surface or one having a greater radius ofcurvature than the die, the edges of the die would engage the pelletfirst and air would become trapped in the space between the faces of thepellet and the die thereby preventing the die from making proper contactwith the pellet and consequently impairing the accuracy of the moulding.The present process ensures that all the air is driven out from thespace between the surfaces of the die and pellet and ensures that thedie makes proper contact with the pellet. Materials such as Perspex areusually cast into sheets but they could readily be originally cast intothe preformed pellets above described.

When the lens has reached a temperature of the order of 20 C. the die 26is raised by means of the lever 33 and the finished lens is ejected fromthe cylinder by raising the die 21 by means of the lever 36. The dies 26and 21 are made of a steel known commercially as a high chrome steel andthey are provided with a degree of polish which is not less than thatfound upon glass lenses which are today used in instruments ofprecision. The dies are of complementary shape to the lens surfaces sothat the moulded lens has the required shape and polish imparted to itduring the moulding operation and is ready for use in an instrument ofprecision when it leaves the mould, without any subsequent grinding orpolishing.

It will be appreciated that any optical devices for use in instrumentsof precision e. g. lenses, prisms or mirrors can readily be formed in asingle moulding operation and that they may be formed integrally withprotecting rims or mounts as desired, a feature which has not heretoforebeen possible owing to the relative movement which has to take placebetween the grinding tool and the optical device produced thereby. Sincethe rim or mount does not have to have an optical surface the surface ofthe sleeve which co-acts with the dies need not be polished and may beof any required shape so as to form screwthreads, milled surfaces,registration devices and the like on the surface of the rim or mount.Examples of some of the device which can be moulded are shown in Figures4-15.

The lens shown in Figure 4 comprises two concave surfaces 41 and 48 anda rim 49. The rim projects outwardly beyond each of the optical faces sothat the lens may be placed face downwardly on a substantially fiatsurface with only the rim touching the surface so that the optical facesare not scratched. The rim is preferably provided with one or moreprojections 50 which may be arranged to co-operate with grooves in thelens-holder to prevent relative rotation between the lens and theholder. As shown in Figure 3, the upper half of the sleeve 40 isprovided with recesses 5| which form the projections 50.

Figures 5, 6 and 7 show respectively a pianoconvex, piano-concave and aconcavo-convex lens formed integrally with a rim 43 which serves toprotect at least one of the optical surfaces. Figures 8 and 9 show adouble convex lens of rectangular form. The optical surfaces 52 and 53are spherical so that at each corner of the surface 53 there is provideda flat portion 60 which serves as a seating for a holder. The surface 52is provided with a protecting rim 49 and one of the edges is formed withprojections 50 as above described, which projections are shown as beingnearer one corner of the lens than the other so as to ensure that thelens is correctly placed in the mount which will have co-operatingrecesses.

Instead of forming a continuous protecting rim completely surroundingthe optical surface, a number of outwardly-directed excrescences may beprovided for the same purpose. A shown in Figures and 11 a lens similarto that shown in Figure 4 may be provided with four equally spacedoutwardly-directed excrescences 54 in place of the outwardly-projectingrim 49. It will be seen that these excrescences serve equally well toprevent the optical surfaces of the lens from being scratched and at thesame time reduce the amount of plastic, material used. The excrescences54 on one side of the lens may be adapted to register with recesses inthe mount and may be arranged as shown in Figure 12, with a differentspace between each pair of excrescences so that the lens can only beplaced in the mount in the correct manner.

A prism, as shown in Figures 13 and 14, may be moulded, by suitablyadapting the dies, so that a protecting rim 49 surrounds each opticalsurface 55 and, as shown in Figure 15, a mirror may likewise be providedwith a protecting rim 49, the reflecting surface of the mirror beingconstituted by a layer of silver upon an optical surface.

The rim which surrounds the optical surface may readily be enlarged toprovide a mount for the device and the mount may be so shaped that thewhole moulding constitutes a self-contained article. As shown in Figure16, an eye-piece for field glasses comprises a double concave lens 55, ascrew-threaded mount 51, and a tapered portion 58 may be moulded as aunitary article. The mount 51 and the tapered portion 58 constitutes aprotecting rim for the lens 55.

I claim:

1. An optical body having an accurate predetermined optical shape formedof a molded transparent resinous material capable of being molded attemperatures not exceeding 200 C. and having two optically polishedsurfaces produced by the operation of molding the material to therequired form by a mold having optically polished molding surfaces, theultimate polish and contour of each of said first-mentioned surfacesbeing those imparted to them by the mold.

2. An optical lens having a predetermined accurate optical shapecomprising a molded body of transparent resinous material which becomesplastic at temperatures not substantially exceeding 160 C., the surfacesof the lens being optically accurate, and said surfaces being theoriginal intact surfaces formed in the molding operation.

3. An optical device comprising a molded optical body of a transparentorganic material having optically accurate surfaces thereon comprisingthe original surfaces imparted thereto from optically polished andaccurately shaped mold surfaces, said device being characterized byhaving a mount for the optical body projecting axially and laterallybeyond some of the boundaries of the optical body and formed integrallywith the optical body and of the same material and adapted to provide asupport for the optical body 568ml HOOIT in the apparatus in which saidbody is to be used.

4. An optical device comprising a molded optical body of a transparentorganic material having optically polished surfaces thereon comprisingthe original surfaces imparted thereto from optically polished andaccurately shaped mold surfaces, said device being characterized byhaving a mount for the optical body projecting axially and laterallybeyond some of the boundaries of the optical body and formed integrallywith the optical body and of the same material and adapted to provide asupport for the optical body in the apparatus in which said body is tobe used and integral retaining means on the mount for interfittingengagement with such apparatus.

5. An optical device comprising a molded optical body of a transparentorganic material havng optically accurate surfaces thereon comprisingthe original surfaces imparted thereto from optically polished andaccurately shaped mold surfaces, said device being characterized byhavng a mounting edge for the optical body extendmg longitudinallybeyond the optical surfaces of the body and formed integrally with andat the same time as the optical body and of the same material andadapted to provide a support whereby the optical body can be directlyintroduced intoi the apparatus in which said body is to be use i 6. Anoptical device comprising a molded optical body of a transparent organicmaterial havng optically accurate surfaces thereon comprising theoriginal surfaces imparted thereto from optically polished andaccurately shaped mold surfaces, said device being characterized byhaving a mount for the optical body projecting radially andlongitudinally beyond some of the boundaries of the optical body andformed integrally with and at the same time as the optical body and ofthe same material and adapted to provide a support whereby the opticalbody can be directly introduced into the apparatus in which said body isto be used.

An optical lens for use in instruments of pre- ClSlOl'l comprising amolded optical body of a transparent organic material having opticallyaccurate surfaces thereon comprising the original surfaces impartedthereto from optically polished and accurately shaped mold surfaces,said lens be ng characterized by having a co-axial cylindrical mount forthe optical body projecting longitudinally beyond an optical surface ofthe optical body and formed integrally with the optical body and of thesame material whereby the mount and optical body are in absolute fixedrelation relative to each other, the mount being adapted to provide asupport for the body in an instrument of precision.

8. An optical device comprising a molded optical body of a transparentorganic material having optically accurate surfaces thereon comprisingthe original surfaces imparted thereto from optically polished andaccurately shaped mold surfaces, said device being characterized byhaving a mount for the optical body projecting axially and radiallybeyond an optical surface of the optical body and being thicker than theadjoining edges of the optical body and formed integrally with theoptical body and of the same material and adapted to provide a supportfor the optical body in the apparatus in which-said body is to be used,and a screw thread adapted to co-act with a groove in said apparatus.

ARTHUR WILLIAM KINGSTON.

